MassGIS Data - 1990 U.S. Census - Blocks

December 1995

Source

This datalayer was produced from the post-census release of 1990 TIGER/Line files for the fourteen counties of Massachusetts. This datalayer includes the boundaries of all census blocks and can therefore be used in conjunction with Census Bureau data summarized at the census block level--the finest available resolution of census data.

The layer is named CENSUS1990BLOCKS_POLY.

Production

Using ArcInfo Workstation, the Census Block data (in coverage format) were created by extracting from county TIGER files all linework, line attributes, and polygon attributes. The coverages were enhanced by dropping redundant data items, appending several demographic data items from the STF-1, STF-3a, and PL94-171 census data matrices, and creating an Arc/INFO ADD file for address-matching. Each polygon in the original county TIGER file was assigned a MassGIS town-ID code, ensuring that all of the original polygons appear within the Town TIGER Geography datalayer.

In some cases, polygons within the TIGER line network were not assigned unique census block numbers by the Census Bureau. That is, more than one polygon was assigned a single census block number, and is thereby related to the same record in the matrices of demographic data published by the Census Bureau. In order to overcome the problem of redundantly assigning data values from the matrices to the TIGER Geography coverages' polygon attribute tables on the basis of these nonunique census block numbers, MassGIS apportioned numeric values among the polygons on the basis of their relative area. This is arguably incorrect, since it assumes demographic heterogeneity among all polygons assigned the same census block number. However, in all cases observed by MassGIS, such polygons were contiguous and relatively small, so the impact of this error is expected to be minimal.